Conventionally, as a power module which has a cooling structure, a configuration equipped with a power semiconductor element, a smoothing capacitor and a metal heat radiating plate radiating heat which is generated by the smoothing capacitor, is indicated (see, for example, Japanese Patent No. 4270864). Furthermore, in the conventional configuration, the metal heat radiating plate is divided into a first domain where the smoothing capacitor is disposed and a second domain where the power semiconductor element is disposed. That is, a conventional power module as shown in FIG. 19 is equipped with a power semiconductor element 1, a smoothing capacitor 21 and a heat radiating plate 5 radiating heat which is generated by the power semiconductor element 1 and the smoothing capacitor 21. And a slit 22 is formed in the heat radiating plate 5, so that the heat which is generated in a first domain 5a at the smoothing capacitor 21 side and the heat which is generated in a second domain 5b at the smoothing capacitor 21 side, are separated thermally. This separation prevents the temperature of the smoothing capacitor 21 from going up by the heat which is generated by the power semiconductor element 1.